This invention relates generally to a torque limited or shear screw for use with an electrical connector, and more particularly, to such a screw which has a torque limiting feature between a head and a body of the screw which must be overcome by force to break the head free from the screw body.
Various types of electrical connectors are used for connecting electrical conductors to one another or to the terminals of electrical devices. Conventional connectors receive a conductor within a channel or the like and then receive a screw. The screw is then tightened against the conductor so that it is held in physical contact with the connector.
In the connector industry, often times shear bolts and screws are used to serve the dual function of securing a wire or conductor in a connector and providing a screw that will break off at some position above the connector housing. There are various disadvantages to current designs of these shear bolts and screws. One disadvantage is that they are expensive to manufacture. Another disadvantage is that such known shear bolts or screws are complex, intricate devices, often being constructed of multiple distinct components. Such construction techniques lead to the higher expense and often unreliable and/or complicated implementation.
Another aspect of known connector assemblies is that the conductors are made of a soft material such as copper or aluminum and may further be defined by a series of individual bare strands. Conventional connectors and, more particularly, screws used with such connectors, may have a tendency to damage the conductors. Pointed, angled or tapered screw configurations often dent or damage the strands.
Connections between connectors and conductors may also involve different materials. For example, the screw of a connector may be made of one material while a conductor may be made of another. Different materials may have different rates of expansion and contraction. Accordingly, the life span of the connection and/or the temperatures to which the connector and conductor may be subject to lead to relative movement between the connector and the conductor. This movement causes loosening of the connection, which leads to an inadequate electrical connection between the parts involved.
Loose connections may also arise from different degrees of elasticity of the parts involved. More particularly, one element may exhibit one degree of elastic deformation during engagement of the screw with the conductor, while another material will exhibit a different degree of elastic deformation. These different degrees of elastic deformation lead to different degrees of material recovery, which may result in loose connections.
Known connectors may be used in areas subject to relatively high degrees of vibration. In such types of environment, vibration may similarly lead to lose connections between the conductor and the connector. More particularly, vibration may lead to movement of the screw relative to the connector. This relative movement, in turn, loosens the physical contact between them. As a way to compensate for this observed loosened connection, a user often performs periodic maintenance to retorque the connection. Without such maintenance, the loose connection may eventually result, for example, in elevated operating temperatures in the connection, which in turn may result in a failed connection. However, such maintenance is either not performed in many situations or, in the case of shear bolts and screws of known designs, cannot be performed because the drive portion of the bolt or screw has been removed.
Therefore, it is desirable to have a connector and a corresponding shear bolt or screw that address the drawbacks of conventional connectors and shear bolts or screws.